SIXTH ANNUAL YEAR BOOK — PART VIII. 787 



essential that the soil be in the condition usually described as fertile. 

 This refers not only to the presence of the required mineral elements 

 but to humus and to a favorable texture. It is not worth while attempt- 

 ing to grow alfalfa upon sterile soil. Such soil should be enriched by 

 the addition of barnyard manure or other fertilizer or by the plowing 

 under of leguminous crops. Compact, cold, or wet soil is unfavorable 

 to the growth of alfalfa, and such soil should be drained and thoroughly 

 aerated by cultivation to reduce it to the proper texture. 



Sandy soil is not usually well adapted to alfalfa, partly because it 

 may be sterile, lacking in humus, or too close in texture. If a stand is 

 once obtained the crop may not suffer from lack of moisture, as there is 

 usually a water supply below the surface? In the Southern States sandy 

 soil is so favorable to the growth of crab grass and other weeds that al- 

 falfa is soon chocked out. In general it is well to prepare sandy soil by 

 incorporating humus and fertilizing and by suitable culture to free from 

 weeds. 



NITROGEN GATHERING NODULES. 



It is well known that alfalfa, in common with other legumes, has up 

 on its roots nodules or tubercles produced by certain bacteria with whose 

 aid the plants are enables to obtain a supply of atmospheric nitrogen. 

 By the decay of these nodules the soil becomes richer in nitrogen. 

 Though alfalfa can grow without the presence of these bacteria, 

 especially if the soil is rich and there is an abundant supply of nitrogen; 

 yet under normal field conditions the growth is much more vigorous 

 when these organisms are present, as indicated by the nodules uopn the 

 roots. The seedling plants are infected or inoculated from the soil if the 

 organisms are present. Where these are not already present it is neces- 

 sary to inoculate the plants artificially in order to produce the best 

 results. This can be done by scattering upon the field soil from an infected 

 field or by placing the bacteria directly upon the seed before sowing. The 

 latter procedure has been rendered practicable by the use of pure cul- 

 tures, a method perfected in the Laboratory of Plant Physiology of the 

 Bureau of Plant Industry of the Department of Agriculture. 



Throughout the region west of the Mississippi River and a consider- 

 able portion of the Eastern States this organism seems to be already 

 widely spread in the soil. At the Illinois Experiment Station it has 

 been shown that the organism upon the roots of the sweet or Bokhara 

 clover (Melilotus alba) products the same effect upon alfalfa as the 

 alfalfa organism itself. Nevertheless the natural inoculation upon the 

 first crop may not be sufficient for its needs. This appears to be snown 

 by the fact that better results are likely to follow sucessive sowings upon 

 the same land. But in any case it must be borne in mind that artificial 

 inoculation of the seed will supply only one of the necessary conditions 

 and will not prevent failure from other causes. 



